This invention relates to mercury metal-halide high-intensity-discharge (HID) lamps and, more particularly, to such lamps which have a relatively warm color appearance coupled with good color rendering and efficacy.
Mercury metal-halide lamps are widely used for area and stadium lighting because of their improved color rendering and efficacy as compared to the usual highpressure mercury and other types of HID lamps. Most mercury metal-halide lamps, however, normally have a color appearance which is relatively "cool" and the color rendition of illuminated objects is not as good as desired.
The internationally accepted method for standardizing and measuring the color rendering properties of light sources is set forth in the publication of the International Commission on Illumination, identified as publication C.I.E. No. 13 (E-1.3.2.) 1965.
Various improvements have been made in mercury metal-halide HID lamps as represented by U.S. Pat. No. 3,786,297, dated Jan. 15, 1974 to Zollweg et al. This patent discloses a mercury metal-halide lamp which includes as essential discharge-sustaining constituents at least one of praseodymium halide, neodymium halide and cerium halide plus cesium halide and mercury in predetermined amount, in addition to the usual starting gas. These essential constituents may be supplemented by other metal halides such as sodium halide, dysprosium halide, and samarium halide.
U.S. Pat. No. 4,029,983, dated June 14, 1977 to Thornton discloses a metal-halide type HID lamp having a light output with incandescent characteristics. The metal halide utilized is the well-known sodium-scandium halide and the resulting discharge is color corrected by the use of a combination phosphor blend of a greenemitting calcium sulfide activated by cerium and redemitting calcium sulfide activated by europium. The blend of phosphors is coated onto the inner surface of the outer protective envelope.
Copending application Ser. No. 841,407, filed Oct. 12, 1977 by Wachtel et al., and owned by the present assignee, sets forth a red-emitting calcium sulfide phosphor which is activated by europium and sensitized by tin, in order to respond to long wavelength ultraviolet radiations, as well as short wavelength ultraviolet radiations. This phosphor is particularly adapted for use with a high-intensity-discharge (HID) lamp wherein the phosphor is used as a coating material applied to the inner surface of the protective envelope which is used with such an HID lamp.